Prior to starting any tests, all pressure transducers and thermocouples were calibrated. This section summarises the calibration procedures followed. The details surrounding the execution of these processes, along with the results that were obtained, are presented in Appendix H.
7.2.1 Throttle actuator calibration
The Posicon 1000 throttle actuator system leaves the factory fully calibrated and does not require recalibration when installed. It was, however, required to set the amount of force exerted by the actuator (this is selected as a percentage of the nominal force rating of the actuator). Apart from the force setting, it was also
y = 6,988x - 0,065 R² = 1 (Pre-Testing) y = 6,984x - 0,001 R² = 1 (Post-Testing) 0 5 10 15 20 25 30 35 40 0 1 2 3 4 5 Tor qu e [N ·m] Voltage [V] Calibration (Pre-Testing) Calibration (Post-Testing) Curve Fit (Pre-Testing) Curve Fit (Post-Testing)
64
required to set the fixed positions for “shut off”, “idle”, and “maximum throttle”. These settings were all performed by following the procedure detailed in the throttle actuator’s user manual.
The final step was to calibrate the feedback signal from the actuator (this was performed directly in ETA) in order to determine the actual position of the actuator from within ETA. During this process, the actual position of the actuator was verified using the hand held remote terminal of the actuator, which displays the actual position of the actuator as a percentage of the stroke between the predefined “idle” and “maximum throttle” positions.
7.2.2 Fuel flow meter calibration
The AVL dynamic fuel balance was calibrated upon installation following the detailed calibration procedure in the fuel flow meter’s user manual. The calibration procedure was directly performed from the fuel flow meter’s control unit. Once the calibration requirements stipulated in the fuel flow meter’s user manual were met, the output from the fuel flow meter’s control unit was calibrated directly in ETA. This ensured that the entire measurement chain was included in the calibration process and that the fuel flow rate displayed in ETA was synchronised with the flow rate displayed by the fuel flow meter’s control unit. Refer to Appendix H.4 for the detailed calibration procedure implemented.
7.2.3 Pressure transducer calibration
7.2.3.1 In-cylinder pressure transducer
During the calibration of the Optrand transducer, a WIKA CPB 3000 dead weight tester was used to apply a known pressure to the sensor. In an effort to achieve the best possible accuracy during the calibration process, the wiring setup, hardware equipment and data logging software was implemented in exactly the same way it was to be used to log data during the engine tests. During calibration, the sensor was electrically connected to the NI 6351 USB data acquisition unit and the sensor output was recorded using LabVIEW software. Refer to Appendix H.2.1 for the calibration results obtained.
7.2.3.2 Intake manifold pressure transducer
The measurement range of -1 to 3 bar gauge pressure of the WIKA S-10 strain gauge pressure transducer required that the sensor be exposed both to vacuum and positive gauge pressure during calibration. The senor was calibrated while being electrically connected exactly the same way it was to be used in service, but without being connected to the damping chamber. The reason for excluding the damping chamber during calibration was due to the chamber adding too much volume to the measurement line, which made it difficult to achieve the required vacuum pressure using the available calibration equipment.
The sensor was calibrated over a pressure range of -0,6 to 1 bar, using a pressure pump from SI Pressure Instruments and a WIKA reference gauge. The upper
65
range of the calibration was restricted to 1 bar due to the test engine not employing force induction. Consequently, the mean intake manifold pressure will not rise higher than atmospheric pressure. The calibration results are presented in Appendix H.2.2.
7.2.3.3 Oil pressure transducer
The A-10 pressure transducer which was used to measure the engine oil pressure was supplied with a calibration certificate. The sensor supplier is ISO certified, therefore the sensor was installed as supplied and the provided sensitivity from the calibration certificate was used to determine the measured pressure. The measurements obtained from the oil pressure sensor is purely for monitoring purposes (in order to verify that there is sufficient oil pressure during start-up and that the oil pressure reading does not abruptly change during operation), therefore using the sensitivity provided on the sensor’s calibration certificate was deemed fit for the purpose.
7.2.4 Temperature sensor calibration
A Fluke 9142 field metrology well was used as heat source during the calibration of the thermocouple sensors. The reference temperature measurement was obtained by employing a calibrated platinum resistance thermometer in conjunction with the field metrology well.
Prior to performing the calibration, the thermocouples were installed as part of the test setup and all the associated wiring to the measurement equipment completed. The thermocouples were then removed from the test setup, with all of their respective wiring harness in place as they would be used as part of the test setup. The sensors were then calibrated with the output values being captured directly in ETA. The field metrology well has a temperature range of -25 °C to 150 °C and the thermocouples were calibrated over a temperature range of 0 °C to 140 °C with data points captured every 20 °C. Upon reaching each of the temperature set point values, the heat source, reference temperature probe and thermocouples were allowed to stabilise before the data was captured. Calibration cycles were performed both while increasing and decreasing the temperature, after which the averages of the measured results were calculated. A first order polynomial was then fitted to the data and used as a calibration curve. Refer to Appendix H.3 for the detailed calibration results.